1. Field of the Invention
The present invention relates to an automobile seat capable of preventing a seat occupant from suffering a whiplash injury when an automotive vehicle has come into a rear-end collision.
2. Description of the Related Art
Automobile seats generally have a headrest mounted on an upper portion of a seat back. When a user sits on a seat, a predetermined clearance is present between the user's head and the headrest, but when an automobile vehicle has come into a rear-end collision, the user's body moves forward, while the user's head remains back. Accordingly, a load is applied to the user's neck, resulting in a whiplash injury.
It is possible to reduce the clearance between the user's head and the headrest to minimize the injury; however, the user's head is often brought into contact with the headrest even in the normal sitting condition, and even a slight movement of the head causes the head to interfere with the headrest, making the user uncomfortable.
A headrest pivotally mounted on a seat back, connected to a pressure portion and always biased rearwards by a coil spring, has been hitherto proposed. When a rear-end collision occurs, the headrest is moved forward by a load inputted to the pressure portion against a biasing force of the coil spring. According to this arrangement, the headrest that has been brought into contact with the head is immediately returned to its original position after the rear-end collision and, hence, a load is also applied to the user's neck (see, for example, Document 1).
Another headrest has been proposed, having a mechanism that acts, in the event of a rear-end collision, to move the headrest forward and hold the headrest at a forward position (see, for example, Document 2 or 3).
Document 1: Japanese Laid-Open Patent Publication No. 2001-39194
Document 2: Japanese Laid-Open Patent Publication No. 2001-163097
Document 3: Japanese Laid-Open Patent Publication No. 2002-274240
The automobile seat as disclosed in Document 2 employs a ratchet mechanism for holding the headrest at the forward position in the event of the rear-end collision. The ratchet mechanism cannot allow the headrest to return to its original position after the rear-end collision. Because the headrest is held at the forward position after the rear-end collision, the impact on the head is reduced to some extent, but it is still insufficient.
The automobile seat as disclosed in Document 3 similarly employs a ratchet mechanism, but this ratchet mechanism is provided with a releasing means that is operable to return the headrest to its original position after the rear-end collision. However, the mechanism is complicated and is hence costly.
Further, when the seat back is inclined rearwardly, if an excessive load is applied to a seat back frame, there is a possibility that a rocking mechanism (whiplash injury-preventing mechanism) may operate unexpectedly.